1. Field of the Invention
The present invention relates to a novel L-glutamic acid producing bacterium and a method for producing L-glutamic acid by fermentation utilizing it. L-glutamic acid is an important amino acid as foodstuffs, drugs and so forth.
2. Description of the Related Art
Conventionally, L-glutamic acid is mainly produced by fermentative methods using so-called L-glutamic acid producing coryneform bacteria belonging to the genus Brevibacterium, Corynebacterium or Microbacterium, or mutant strains thereof (Amino Acid Fermentation, pp. 195–215, Gakkai Shuppan Center, 1986).
It is known that, in the production of L-glutamic acid by fermentation, trehalose is also produced as a secondary product. Therefore, techniques have been developed for decomposing or metabolizing the produced trehalose. Such techniques include the method of producing an amino acid by fermentation using a coryneform bacterium in which proliferation ability on trehalose is induced (Japanese Patent Laid-open (Kokai) No. 5-276935) and the method of producing amino acid by fermentation using a coryneform bacterium in which a gene coding for trehalose catabolic enzyme is amplified (Korean Patent Publication (B1) No. 165836). However, it is not known how to suppress the formation of trehalose itself in an L-glutamic acid producing bacterium.
In Escherichia coli, the synthesis of trehalose is catalyzed by trehalose-6-phosphate synthase. This enzyme is known to be encoded by otsA gene. Further, it has been also reported that an otsA gene-disrupted strain of Escherichia coli can scarcely grow in a hyperosmotic medium (H. M. Glaever, et al., J. Bacteriol., 170(6), 2841–2849. (1998)). However, the relationship between disruption of otsA gene and production of substances has not been known.
On the other hand, although the treY gene is known for Brevibacterium helvolum among bacteria belonging to the genus Brevibacterium bacteria, any otsA gene is not known for them. As for bacteria belonging to the genus Mycobacterium bacteria, there is known a pathway via a reaction catalyzed by a product encoded by treS gene (trehalose synthase (TreS)), which gene is different from the otsA gene and treY gene, as a gene coding for a enzyme in trehalose biosynthesis pathway (De Smet K. A., et al., Microbiology, 146 (1), 199–208 (2000)). However, this pathway utilizes maltose as a substrate and does not relate to usual L-glutamic acid fermentation that utilizes glucose, fructose or sucrose as a starting material.